1. Field of the Invention
The present invention relates to an elastic wave branching filter.
2. Description of the Related Art
In recent years, elastic wave branching filters using elastic waves, such as surface acoustic waves and boundary acoustic waves, have been widely used in communication devices, such cellular phones. For example, Japanese Unexamined Patent Application Publication No. 2008-5151 discloses a surface acoustic wave branching filter illustrated in FIG. 8.
As illustrated in FIG. 8, a surface acoustic wave branching filter 100 includes a transmission filter 104 connected between an antenna terminal 101 and a transmitting terminal 102 and a reception filter 105 connected between the antenna terminal 101 and receiving terminals 103a and 103b. In the surface acoustic wave branching filter 100, the reception filter 105 is formed by a longitudinally coupled resonator-type surface acoustic wave filter. A surface acoustic wave resonator 106 is connected between the reception filter 105 and the antenna terminal 101. With the provision of the surface acoustic wave resonator 106, it is possible to adjust the phase difference between the transmission filter 104 and the reception filter 105.
However, the reception filter 105 of the surface acoustic wave branching filter 100 has a nonlinear characteristic, and thus IMD (Intermodulation Distortion) occurs. For example, if the frequency of an interference wave signal input from the antenna terminal 101 matches the value calculated from a numerical formula of (frequency of transmitted signal×2-frequency of received signal), the frequency of IMD generated from the transmitted signal and the interference wave signal matches the frequency of the received signal. Therefore, there is a problem of deterioration of the sensitivity of the received signal.